1. Field of the Invention
The present invention relates to a signal transmission system, and more particularly to such a system for use in an endoscope including a solid state image sensor.
2. Description of the Prior Art
An endoscope has been proposed which employs a solid state image sensor or imaging device, which may be a charge transfer device (CTD), such as a charge coupled device (CCD) and a bucket brigade device (BBD), in the interest of compactness and economy. In general, an imaging device is provided in a viewing head that is to be inserted into a cavity or opening of a living body or machinery to pick up an image of an inside part of the cavity, when driven in a raster scanning fashion, to produce a video signal representative of the image picked up. The video signal is transmitted to a video display device and in turn visualized thereon as a picture indicative of the picked up image.
Endoscopes may often be used under the circumstances where electromagnetic waves are present to such an extent so as to adversely effect noise on video signals produced from an imaging device and transmitted to a video display, causing dots, stripes and smears to appear in a picture displayed.
Specifically in the case of a medical endoscope, an instrument such as a surgical scalpel may be provided in a viewing head to operate on an affected part of a living body. In particular, an electrical scalpel or surgical knife may often be used, which is driven by a high frequency current, which is conducted into an affected part to generate the Joule's heat therein, allowing the cutting out, taking out or incising of the affected part.
A conventional endoscope employing a solid state image sensor together with an electrical instrument such as a high frequency surgical scalpel has a problem that an electromagnetic coupling may occur between an electrical connection associated with the electrical forceps and another electrical connection associated with the image sensor. Specifically, video signals which are analog signals in a baseband produced by the imaging device may often be affected, while transmitted on the electrical connection to a display system, by noise induced from the other electrical connection associated with the electrical forceps, since the electrical connection for transmitting video signals thereon is substantially in parallel in a sheath of the endoscope with the electrical connection for supplying power at a high frequency to the electrical forceps. Consequently, it is difficult to visualize the video signals on a video display as a clear picture suitable for diagnosis of the affected portion. Situation is similar in the case of some industrial fields which are full of electromagnetic waves, as in a welding cite, etc.